ruby 1.9.* does not respect respond_to? :to_ary when calling flatten

gistfile1.rb

def test_config klass
  var = klass.new
  unless !var.respond_to?(:to_ary) && [var].flatten == [var]
    puts "#{klass.name} is misbehaved"
  end
end

class RespondToMissingTest
  def respond_to_missing? method, *rest
    if method.to_sym == :to_ary
      false
    else
      super
    end
  end

  def method_missing *args
    args
  end
end

class RespondToTest
  def respond_to? method, *rest
    if method.to_sym == :to_ary
      false
    else
      super
    end
  end

  def method_missing *args
    args
  end
end

class MethodButNonResponsiveTest
  def to_ary
    raise NoMethodError
  end

  def respond_to? method, *rest
    if method.to_sym == :to_ary
      false
    else
      super
    end
  end
end

test_config RespondToMissingTest
test_config RespondToTest
test_config MethodButNonResponsiveTest